Artificial Rock Sculpting Tutorial Part 2
Texture and detail will give the artificial rock a natural look
You want to end up with a basic overall smooth effect where all the holes, divots and air bubbles from applying the concrete by hand are smoothed out leaving a relatively flat surface. Continue dipping the trowel in water and smoothing out the concrete as much as possible. This will allow you to easily imprint textures from the texturing mats.
Remember that you are trying to maintain a minimum thickness of 1.5 to 3 inches, and you can check this by slicing your point trowel straight into the concrete and judge by how far it enters before it reaches the steel frame of your form. You will almost certainly have too much concrete near the base and not enough in the difficult to apply regions like vertical surfaces. Work to remove excess from some areas and apply more to others. This will ensure that your end product is equally strong throughout.
Once you have covered your form in concrete and the total structure seems to be stable you can begin the detail sculpting process.
When sculpting your artificial rock at this point you can begin to add clumps of concrete in a row to create dramatic ridges and cracks. You can also cut out sections where the concrete is thick enough to allow to make fractures and veins in the rock.
How to use a texture mat to exactly re-create natural rock
Since a texture mat is a mold taken from a real stone, the end result is a perfect recreation of the texture and detail found in naturally occurring stone. The concrete should be fully smoothed out and without air bubbles. Ideally you will want the concrete to be slightly cured since concrete that is too wet still will not accept the texture very well.
You will spray release agent onto your texture mat, and also a small amount on the area you are going to texture on the artificial rock. Gently press the center of the texture mat into place and roll outward to all the edges to avoid dragging any part of the mat across the concrete. Once in place you will pat the texture mat into the concrete being sure to apply even pressure throughout. The more dry the concrete at this stage, the more force you will need to use to pat the pattern into the cement.
Tips and tricks for artificial rock sculpting
You can add ridges and cracks by hand to your artificial rock by slicing a line in the concrete with your point trowel. Add new concrete to only one side of the line. What you are trying to do is build a smooth, sharp ridge that stands vertically taller on one side than the other.
This type of sculpting will reflect a major crack in the rock and can be done with great success. It will take practice in order to create realistic fissures and faults by hand. Having a solid understanding of how rock forms, breaks and wears will aid you in this. You can emphasize the cracks imprinted with the texture mat to create a more dramatic effect. With practice you can create ridges and fissures on top of each other creating a worn and aged look in your stone but if you want your initial projects to be as realistic as possible, keep it very simple.
There is another technique that you can implement to help create the illusion of natural rock. Using a sea sponge you can lightly, and also not so lightly, dab areas of the open surface to give a pock marked weather deteriorated effect. You can even use the pressure of pushing with the sea sponge to create new, slightly dramatic edges and fissures. Blotching with the sea sponge is a great trick to hide any imperfections or rough areas in your work.
Do some experimenting and try a few different techniques, but bear in mind that the workability of the concrete is limited by time and you must commit to an overall shape before too long. Any details left unattended will be permanently reflected in the hardened concrete.
The texture itself is very difficult to show in photograph as seen in the examples below. In person, the concrete takes on the exact minute detail present in real rock. Since concrete resembles the qualities of stone so closely to begin with, once you apply these detailing and texturing techniques the end result is virtually identical to real rock.
Remember to wash EVERYHTING before you quit for the day as the concrete will ruin anything left in contact with it. As the final step once you are completely finished sculpting is to mist the rock down with a light coating of water and cover with plastic.
Remember that concrete itself has acidic properties so be sure to wear protective clothing at all times and wash off any concrete that comes in contact with your skin. Some people have more tolerance to this acid than others, but concrete burn can be very unpleasant so err on the side of caution at all times.
Take a look at this example of a more dramatic artificial rock. Once you are comfortable with the process and techniques of a basic artificial rock you can begin to create more dramatic and custom designs by hand.
Leave your project for 3 entire days as the absolute minimum before beginning the next step being sure to admire your handiwork and contemplate how you will improve on your next attempt. Be sure to mist with water at least 2 to 3 times per day. More if hot or in direct sunlight as this will stop the concrete from drying out too quickly which would otherwise result in hairline cracking.
You will be excited to know that the next step is the one where your artificial rock REALLY starts to take on the characteristics or real stone! Letís take a look at the final preparation stage of artificial rock construction: